The invention relates to a reel of the kind in which a belt, for example a vehicle seat belt, can be wound, and from which the belt may be unwound for use.
It is desirable that the belt be coiled on a shaft of the reel in a regular spiral configuration, without radial protrusions, so that winding and unwinding are smooth, continuous operations. This is made difficult by the need to secure one end of the belt to the shaft, as the securement means tends to produce a hump at at least one position around the shaft. If the belt end is secured within the interior of a hollow shaft of circular cross-section, the belt extending outwardly of a slot in the shaft wall, the belt still cannot be smoothly coiled on the shaft because of the discontinuity at the position at which the belt emerges from the slot.
In U.S. Pat. No. 4,008,863, issued on Feb. 22, 1977 to Arthur Fohl, a solution to this problem is proposed according to which a belt winding-up roller system has a winding-up shaft means with an outer contour in the path of an Archimedes spiral having a pitch corresponding to the thickness of the belt, the belt being wound on the shaft means starting at the point of smallest radius and proceeding about the spiral surface to the point of greatest radius, the contacting surface of the belt with the shaft means and with itself lying in the path of the Archimedes spiral.
This solution provides for the desired smooth rolling up and unrolling of the belt but is accompanied by serious manufacturing difficulties. These arise from the specified external shape of the shaft means, the attainment of which requires the use of expensive specialized machinery. If the external shape of the shaft means is provided by a moulded plastics sleeve, this difficulty applies to the preparation of the mould. The mould may be produced by spark erosion techniques and this requires an electrode to be produced in the shape of the sleeve to be moulded, so this electrode cannot be produced by conventional means and is consequently unduly expensive.
It is accordingly an object of the invention to provide a belt reel with a support surface on and from which a belt can be smoothly wound and unwound, which can be economically produced.
It is also an object of the invention to provide a belt reel with a shaft on and from which a belt can be smoothly wound and unwound, the shape of the shaft outer surface being geometrically simple.